What causes the induced voltage across the coil in a crankshaft position sensor?

The induced voltage across the coil in a crankshaft position sensor is primarily caused by the movement of a tab passing through the magnetic field. In this type of sensor, a magnetic field is established either by a permanent magnet or an electromagnet. As the tab, which is part of the crankshaft, moves through this magnetic field, it alters the magnetic flux linking the coil.

According to Faraday's law of electromagnetic induction, a change in magnetic flux induces a voltage in the coil. Therefore, when the tab moves, it causes a variation in the magnetic field around the coil, resulting in an induced voltage. This induced voltage is what the sensor detects and uses to determine the position and speed of the crankshaft, which is critical for engine timing and performance.

The other options do not directly account for the phenomenon of induced voltage in this context, as they either describe factors unrelated to the actual induction process or do not encompass the essential movement aspect that drives the induction in the crankshaft position sensor.